Superoxide dismutase and Parkinson's disease

Oxidation of dopamine and related catechols in dopaminergic brain regions in Parkinson's disease and during ageing in non-Parkinsonian subjects

The present study was performed to examine if catechol oxidation is higher in brains from patients with Parkinson's disease compared to age-matched controls, and if catechol oxidation increases with age. Brain tissue from Parkinson patients and age-matched controls was examined for oxidation of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylalanine (DOPA) to corresponding quinones, by measurement of 5-S-cysteinyl-dopamine, 5-S-cysteinyl-DOPAC and 5-S-cysteinyl-DOPA. The cysteinyl catechols are assumed to be biomarkers for DA, DOPAC and DOPA autoxidation and part of the biosynthetic pathway of neuromelanin. The concentrations of the 5-S-cysteinyl catechols were lower, whereas the 5-S-cysteinyl-DA/DA and 5-S-cysteinyl-DOPAC/DOPAC ratios tended to be higher in the Parkinson group compared to controls, which was interpreted as a higher degree of oxidation. High 5-S-cysteinyl-DA/DA ratios were found in the substantia nigra of a sub-population of the Parkinson group. Based on 5-S-cysteinyl-DA/DA ratios, dopamine oxidation was found to increase statistically significantly with age in the caudate nucleus, and non-significantly in the substantia nigra. In conclusion, the occurrence of 5-S-cysteinyl-DA, 5-S-cysteinyl-DOPAC and 5-S-cysteinyl-DOPA was demonstrated in dopaminergic brain areas of humans, a tendency for higher oxidation of DA in the Parkinson group compared to controls was observed as well as a statistically significant increase in DA oxidation with age. Possibly, autoxidation of DA and other catechols are involved in both normal and pathological ageing of the brain. This study confirms one earlier but small study, as well as complements one study on non-PD cases and one study on both PD cases and controls on NM bound or integrated markers or catechols.

Metabolic Dysfunction in Parkinson's Disease: Bioenergetics, Redox Homeostasis and Central Carbon Metabolism

The loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of protein inclusions (Lewy bodies) are the pathological hallmarks of Parkinson's disease (PD). PD is triggered by genetic alterations, environmental/occupational exposures and aging. However, the exact molecular mechanisms linking these PD risk factors to neuronal dysfunction are still unclear. Alterations in redox homeostasis and bioenergetics (energy failure) are thought to be central components of neurodegeneration that contribute to the impairment of important homeostatic processes in dopaminergic cells such as protein quality control mechanisms, neurotransmitter release/metabolism, axonal transport of vesicles and cell survival. Importantly, both bioenergetics and redox homeostasis are coupled to neuro-glial central carbon metabolism. We and others have recently established a link between the alterations in central carbon metabolism induced by PD risk factors, redox homeostasis and bioenergetics and their contribution to the survival/death of dopaminergic cells. In this review, we focus on the link between metabolic dysfunction, energy failure and redox imbalance in PD, making an emphasis in the contribution of central carbon (glucose) metabolism. The evidence summarized here strongly supports the consideration of PD as a disorder of cell metabolism.

Complex deregulation and expression of cytokines and mediators of the immune response in Parkinson's disease brain is region dependent

Neuroinflammation is common in neurodegenerative diseases including Parkinson disease (PD). Expression of 25 mRNAs was assessed with TaqMan-PCR including members of the complement system, colony stimulating factors, Toll family, cytokines IL-8, IL-6, IL-6ST, IL-1B, TNF-α family, IL-10, TGFβ family, cathepsins and integrin family, in the substantia nigra pars compacta, putamen, frontal cortex area 8 and angular gyrus area 39, in a total of 43 controls and 56 cases with PD-related pathology covering stages 1-6 of Braak. Up-regulation of IL-6ST was the only change in the substantia nigra at stages 1-2. Down-regulation of the majority of members examined occurred in the substantia nigra from stage 4 onwards. However, region-dependent down- and up-regulation of selected mRNAs occurred in the putamen and frontal cortex, whereas only mRNA up-regulated mRNAs were identified in the angular cortex from stage 3 onwards in PD cases. Protein studies in frontal cortex revealed increased IL6 expression and reduced IL-10 with ELISA, and increased IL-6 with western blotting in PD. Immunohistochemistry revealed localization of IL-5, IL-6 and IL-17 receptors in glial cells, mainly microglia; IL-5, IL-10 and M-CSF in neurons; TNF-α in neurons and microglia; and active NF-κB in the nucleus of subpopulations of neurons and glial cells in PD. Distinct inflammatory responses, involving pro- and anti-inflammatory cytokines, and variegated mediators of the immune response occur in different brain regions at the same time in particular individuals. Available information shows that altered α-synuclein solubility and aggregation, Lewy body formation, oxidative damage and neuroinflammation converge in the pathogenesis of PD.

The Rich Electrochemistry and Redox Reactions of the Copper Sites in the Cellular Prion Protein

This paper reviews recent electrochemical studies of the copper complexes of prion protein (PrP) and its related peptides, and correlates their redox behavior to chemical and biologically relevant reactions. Particular emphasis is placed on the difference in redox properties between copper in the octarepeat (OR) and the non-OR domains of PrP, as well as differences between the high and low copper occupancy states in the OR domain. Several discrepancies in literature concerning these differences are discussed and reconciled. The PrP copper complexes, in comparison to copper complexes of other amyloidogenic proteins/peptides, display a more diverse and richer redox chemistry. The specific protocols and caveats that need to be considered in studying the electrochemistry and redox reactions of copper complexes of PrP, PrP-derived peptides, and other related amyloidogenic proteins are summarized.

Redox reactions of the α-synuclein-Cu(2+) complex and their effects on neuronal cell viability

α-Synuclein (α-syn), a presynaptic protein believed to play an important role in neuropathology in Parkinson's disease (PD), is known to bind Cu(2+). Cu(2+) has been shown to accelerate the aggregation of α-syn to form various toxic aggregates in vitro. Copper is also a redox-active metal whose complexes with amyloidogenic proteins/peptides have been linked to oxidative stress in major neurodegenerative diseases. In this work, the formation of the Cu(2+) complex with α-syn or with an N-terminal peptide, α-syn(1-19), was confirmed with electrospray-mass spectrometry (ES-MS). The redox potentials of the Cu(2+) complex with α-syn (α-syn-Cu(2+)) and α-syn(1-19) were determined to be 0.018 and 0.053 V, respectively. Furthermore, the Cu(2+) center(s) can be readily reduced to Cu(+), and possible reactions of α-syn-Cu(2+) with cellular species (e.g., O(2), ascorbic acid, and dopamine) were investigated. The occurrence of a redox reaction can be rationalized by comparing the redox potential of the α-syn-Cu(2+) complex to that of the specific cellular species. For example, ascorbic acid can directly reduce α-syn-Cu(2+) to α-syn-Cu(+), setting up a redox cycle in which O(2) is reduced to H(2)O(2) and cellular redox species is continuously exhausted. In addition, the H(2)O(2) generated was demonstrated to reduce viability of the neuroblastoma SY-HY5Y cells. Although our results ruled out the direct oxidation of dopamine by α-syn-Cu(2+), the H(2)O(2) generated in the presence of α-syn-Cu(2+) can oxidize dopamine. Our results suggest that oxidative stress is at least partially responsible for the loss of dopaminergic cells in PD brain and reveal the multifaceted role of the α-syn-Cu(2+) complex in oxidative stress associated with PD symptoms.

Increased oxidation of certain glycolysis and energy metabolism enzymes in the frontal cortex in Lewy body diseases

Lipoxidative damage of aldolase A, enolase 1, and glyceraldehyde dehydrogenase (GAPDH) was found in the frontal cortex in a percentage of aged controls by bidimensional gel electrophoresis, Western blot test, in-gel digestion, and mass spectrometry. Aldolase A and enolase 1 were altered in 12 of 19 cases, whereas oxidation of GAPDH was found in 6 of 19 controls. The three enzymes were oxidized in the frontal cortex in the majority of cases of incidental Parkinson's disease (iPD), PD, and dementia with Lewy bodies (DLB). Differences were statistically significant (chi(2) test) for GAPDH in PD and DLB. Densitometric studies have shown that the ratio of oxidized protein per spot is higher in iPD, PD, and DLB compared with controls. These findings show oxidation of three enzymes linked with glycolysis and energy metabolism in the adult human brain as well as increased oxidation of aldolase A, enolase 1, and GAPDH in the frontal cortex in Lewy body diseases. Modifications of these enzymes may result in decreased activity and may partly account for impaired metabolism and function of the frontal lobe in PD.

Early α-synuclein lipoxidation in neocortex in Lewy body diseases

Previous studies in Lewy body diseases (LBDs), including Parkinson's disease (PD) and Dementia with Lewy bodies (DLB), have shown oxidative stress damage more extended than the expected for the distribution of Lewy pathology. Since malondialdehyde (MDA) can form adducts with lysine residues of proteins, MDA-Lys immunoprecipitation and alpha-synuclein immunoblotting has been carried out in frontal cortex and substantia nigra homogenates from five patients with PD, five DLB, three iPD and seven aged-matched controls to decipher the extent of lipoxidized alpha-synuclein in LBDs. MDA-Lys-lipoxidation of alpha-synuclein in the substantia nigra and frontal cortex has been found in all DLB and PD cases examined, but also in the frontal cortex in 3/3 and in the substantia nigra in 2/3 cases with iPD. In addition, one control case had MDA-Lys-modified alpha-synuclein in the frontal cortex, and another in the substantia nigra. This work provides evidence of extended lipoxidative modification of alpha-synuclein in LBDs. Moreover, it demonstrates that alpha-synuclein lipoxidation is an early event in LBDs which precedes alpha-synuclein solubility modification and aggregation, and formation of Lewy bodies and neurites.

Evidence of oxidative stress in the neocortex in incidental Lewy body disease

Oxidative stress has been well documented in the substantia nigra in Parkinson disease (PD), but little is known about oxidative damage, particularly lipoxidation, advanced glycation (AGE), and AGE receptors (RAGE) in other structures, including the cerebral cortex, in early stages of diseases with Lewy bodies. The present study was undertaken to analyze these parameters in the frontal cortex (area 8), amygdala, and substantia nigra in selected cases with no neurologic symptoms and with neuropathologically verified incidental Lewy body disease-related changes, comparing them with healthy age-matched individuals. Results of the present study have shown mass spectrometric and immunologic evidences of increased lipoxidative damage by the markers malondialdehyde-lysine (MDAL) and 4-hydroxynonenal-lysine (HNE), increased expression of AGE in the substantia nigra, amygdala, and frontal cortex, and increased and heterogeneous RAGE cellular expression in the substantia nigra and frontal cortex in cases with early stages of parkinsonian neuropathology. In addition, increased content of the highly peroxidizable docosahexaenoic acid in the amygdala and frontal cortex. These changes were not associated to alpha-synuclein aggregation in cortex, contrasting with aggregates found in SDS-soluble fractions of frontal cortex in dementia with Lewy bodies (DLB) cases. The pattern of lipidic abnormalities differed in DLB and incidental Lewy body disease. Furthermore, although AGE and RAGE expression were raised in DLB, no increase in the total amount of HNE and MDAL adducts was found in the cerebral cortex in DLB. Preliminary analyses have identified 2 proteins with lipoxidative damage, alpha-synuclein and manganese superoxide dismutase (SOD2), in incidentally Lewy body disease cortex. This study demonstrates abnormal fatty acid profiles, increased and selective lipoxidative damage, and increased AGE and RAGE expression in the frontal cortex in cases with early stages of parkinsonian neuropathology without treatment. These findings further support antioxidant therapy in the treatment of PD to reduce cortical damage associated with oxidative stress.

Fibroblasts derived from Gpx1 knockout mice display senescent-like features and are susceptible to H2O2-mediated cell death

The Free Radical Theory of Aging proposes that reactive oxygen species (ROS) contribute to the pathophysiology of aging. Our previous data highlight the importance of antioxidant enzymes, superoxide dismutase 1 (Sod1) and glutathione peroxidase 1 (Gpx1), in regulating this process. Previously, we demonstrated that a perturbation in the Sod1-to-Gpx1 ratio, as a consequence of Sod1 overexpression, leads to senescence-like changes. We proposed that this was mediated via the Sod1 dismutation product H2O2, because H2O2 induced similar changes in control cells. However, it has been suggested that H2O2 production, via Sod1 dismutation, is rate-limited by the availability of the substrate O2*-, and therefore age-related changes may occur as a result of other functions of Sod1. In this study, we test this notion in fibroblasts derived from Gpx1 null mutant mice (Gpx1-/-) that have elevated H2O2 as a consequence of the lack of its removal by Gpx1. We demonstrate senescence-like changes in Gpx1-/- fibroblasts that include (1) reduced proliferative capacity, DNA synthesis, and responsiveness to EGF and serum; (2) elevated levels of Cip1; (3) increased NF-kappaB activation; and (4) morphological features of senescent cells. Gpx1-/- fibroblasts also demonstrate a dose-dependent susceptibility to H2O2-induced apoptosis. Our findings suggest that Gpx1 is protective against both ROS-mediated senescence-like changes and oxidant-mediated cell death.

Alterations in m-RNA expression for Cu,Zn-superoxide dismutase and glutathione peroxidase in the basal ganglia of MPTP-treated marmosets and patients with Parkinson's disease

Alterations occurring in the antioxidant enzymes, copper, zinc-dependent superoxide dismutase (Cu,Zn-SOD) and glutathione peroxidase (GPX) following nigral dopaminergic denervation are unclear. We now report on the distribution and levels of m-RNA for Cu,Zn-SOD and GPX in basal ganglia of normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, and in normal individuals and patients with Parkinson's disease (PD) using in situ hybridization histochemistry and oligodeoxynucleotide (single-stranded DNA) probes. Cu,Zn-SOD and GPX m-RNA was present throughout basal ganglia (nucleus accumbens, caudate-putamen, globus pallidus, substantia nigra) in the common marmoset, with the highest levels being in substantia nigra (SN). Following MPTP induced nigral cell loss, Cu,Zn-SOD m-RNA levels were decreased in all areas but the SNr, and particularly in SNc (71%, P<0.001). MPTP-treatment had no effect on GPX m-RNA expression in any area of basal ganglia. Cu,Zn-SOD and GPX m-RNA was also present in the normal human SN. In PD, however, Cu,Zn-SOD m-RNA was significantly decreased (89%, P<0.005) in SNc, and there was a near-complete loss of GPX m-RNA in both SNc (100%, P<0.005) and SNr (88%, P<0.005). The loss of Cu,Zn-SOD m-RNA in SNc in MPTP-treated marmosets and patients with PD suggests that it is primarily located in dopaminergic neuronal cell bodies. The loss of GPX m-RNA in SNc in PD also suggests a localisation to dopaminergic cell bodies, but the similar change in SNr may indicate its presence in dopaminergic neurites. In contrast, the absence of change in GPX m-RNA in MPTP-treated primates appears to rule out its presence in dopaminergic cells in this species, but this may only be apparent and may reflect increased expression in glial cells following acute toxin treatment.

The distribution of copper, zinc- and manganese-superoxide dismutase, and glutathione peroxidase messenger ribonucleic acid in rat basal ganglia

Oxidative stress may contribute to the progression of Parkinson's disease, and while the status of antioxidant enzymes is thus important, little data on their regional distribution in basal ganglia exist. We now report on the distribution and levels of messenger ribonucleic acid (m-RNA) for the antioxidant enzymes copper, zinc-superoxide dismutase (Cu,Zn-SOD), manganese-superoxide dismutase (Mn-SOD), and glutathione peroxidase in rat basal ganglia using in situ hybridisation histochemistry with complementary deoxyribonucleic acid probes specific for these enzymes. The m-RNA for Cu,Zn-SOD, Mn-SOD, and glutathione peroxidase was expressed throughout basal ganglia. Levels of m-RNA were significantly higher in substantia nigra pars compacta than in all other regions of basal ganglia for both Cu,Zn-SOD (53-62%, P<0.001) and Mn-SOD (37-45%, P<0.05). Mn-SOD m-RNA levels were also significantly higher in SN pars reticulata than in the nucleus accumbens (10%, P<0.05) and striatum (12%, P<0.01). In contrast, glutathione peroxidase m-RNA levels were only significantly higher in SN pars compacta when compared with SN pars reticulata (23%, P<0.05), and in the striatum when compared with the nucleus accumbens (21%, P<0.05). The data suggest that SN pars compacta may be vulnerable to oxidative stress and thus dependent on the high antioxidant capacity provided by these cytoprotective enzymes. In conclusion, this study demonstrates the relative distribution of antioxidant enzymes in rat basal ganglia and forms the basis for further study in rodent models of Parkinson's disease.

6-Hydroxydopamine-lesioning of the nigrostriatal pathway in rats alters basal ganglia mRNA for copper, zinc- and manganese-superoxide dismutase, but not glutathione peroxidase

The effects of nigrostriatal pathway destruction on the mRNA levels of copper, zinc-dependent superoxide dismutase (Cu,Zn-SOD), manganese-dependent superoxide dismutase (Mn-SOD), and glutathione peroxidase in basal ganglia of adult rat were investigated using in situ hybridization histochemistry and oligodeoxynucleotide (single-stranded complementary DNA) probes. The 6-hydroxydopamine (6-OHDA)-induced destruction of the nigrostriatal pathway resulted in contralateral rotation to apomorphine and a marked loss of specific [(3)H]mazindol binding in the striatum (93%; P<0.05) and of tyrosine hydroxylase mRNA in substantia nigra pars compacta (SC) (93%; P<0.05) compared with control rats. Levels of Cu,Zn-SOD mRNA were decreased in the striatum, globus pallidus, and SC on the lesioned side of 6-OHDA-lesioned rats compared with sham-lesioned rats (P<0.05). Levels of Mn-SOD mRNA were increased in the nucleus accumbens (P<0.05), but decreased in the SC (P<0.05) on the lesioned side of 6-OHDA-treated rats compared with sham-lesioned rats. Lesioning with 6-OHDA had no effect on glutathione peroxidase mRNA levels in any region of basal ganglia examined. The significant changes in Cu,Zn-SOD and Mn-SOD mRNA indicate that SOD is primarily expressed by dopaminergic neurons of the nigrostriatal pathway, and that the Mn-SOD gene appears to be inducible in rat basal ganglia in response to both physical and chemical damage 5 weeks after 6-OHDA-lesioning. These findings may clarify the status of antioxidant enzymes, particularly Mn-SOD, in patients with Parkinson's disease and their relevance to disease pathogenesis.

Evidence of functional zinc deficiency in Parkinson's disease

One of the primary areas of investigation in the pathophysiology of Parkinson's disease (PD) is the loss of the dopamine-producing cells in the melanized neurons of the substantia nigra, believed to be caused by oxidative stress resulting from excessive free radical activity. The cuprozinc enzyme, superoxide dismutase (SODCu2Zn2), catalyzes the dismutation of superoxide anions to hydrogen peroxide plus oxygen, and is normally found in high concentrations in the substantia nigra where it protects neurons by scavenging free radicals. Zinc supplementation has been shown to significantly increase SODCu2Zn2 in vitro. A novel oral zinc tally test (ZTT) used in the assessment of zinc status was administered to 100 PD patients and 25 controls. Patients with PD showed a significantly decreased zinc status as compared to controls (p < 0.001). Significance was also established for 3 self-reported health-related variables thought to be related to zinc status: vision problems, olfactory loss, and taste loss (p < 0.05). Relative risks for patients with PD for these variables were 1.51, 1.56, and 1.33, respectively. Zinc status as measured by the ZTT is negatively correlated with PD status. PD status is positively correlated with self-reported vision problems, and olfactory and taste loss. Further study of the role of zinc in the development and treatment of PD is warranted.

Effects of pergolide treatment on in vivo hydroxyl free radical formation during infusion of 6-hydroxydopamine in rat striatum

This study focused on the early neurochemical events involved in 6-hydroxydopamine (6-OHDA) neurotoxicity and the putative neuroprotective effects of pergolide. 6-OHDA in 0.1% ascorbic acid/saline was delivered into rat striatum by means of microdialysis and 2,3-dihydroxybenzoic acid (2,3-DHBA) was measured as an index of hydroxyl free radical formation using salicylate trapping. Infusion of 6-OHDA (2-20 mM) via the dialysis probe for 15 min was associated with an immediate and striking increase in the extracellular levels of 2,3-DHBA and dopamine, and this effect was dose-dependent. An infusion of 10 mM 6-OHDA, equivalent to a direct injection of approximately 4 microgram free base, resulted in dopamine overflow with a maximum approx. 200-fold above the baseline. This massive overflow of toxic amounts of dopamine, much greater than expected of reuptake inhibition, seems to be the earliest response of nigrostriatal neurones to 6-OHDA. In rats treated with pergolide mesylate (7 days 0.5 mg/kg/day, i.p.), the average amount of 2, 3-DHBA associated with 6-OHDA striatal infusion was significantly smaller than that in controls. This suggests that pergolide treatment leads to an increased ability of striatal tissue to quench hydroxyl radical formation in vivo.

Mitochondrial impairment as an early event in the process of apoptosis induced by glutathione depletion in neuronal cells: relevance to Parkinson's disease

In Parkinson's disease (PD), dopaminergic cell death in the substantia nigra was associated with a profound glutathione (GSH) decrease and a mitochondrial dysfunction. The fall in GSH concentration seemed to appear before the mitochondrial impairment and the cellular death, suggesting that a link may exist between these events. The relationships between GSH depletion, reactive oxygen species (ROS) production, mitochondrial dysfunction and the mode of cell death in neuronal cells remain to be resolved and will provide important insights into the etiology of Parkinson's disease. An approach to determine the role of GSH in the mitochondrial function and in neurodegeneration was to create a selective depletion of GSH in a neuronal cell line in culture (NS20Y) by inhibiting its biosynthesis with L-buthionine-(S,R)-sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase. This treatment led to a nearly complete GSH depletion after 24 hr and induced cellular death via an apoptotic pathway after 5 days of BSO treatment. By using the reactive oxygen species-sensitive probe 2',7'-dichlorofluorescin, we observed that the rapid GSH depletion was accompanied, early in the process, by a strong and transient intracellular increase in reactive oxygen species evidenced after 1 hr with BSO, culminating after 3 hr when the GSH level decreased to 30% of normal. GSH depletion induced a loss of mitochondrial function after 48 hr of BSO treatment. In particular, the activities of complexes I, II and IV of the respiratory chain were decreased by 32, 70 and 65%, respectively as compared to controls. These results showed the crucial role of GSH for maintaining the integrity of mitochondrial function in neuronal cells. Oxidative stress and mitochondrial impairment, preceding DNA fragmentation, could be early events in the apoptotic process induced by GSH depletion. Our data are consistent with the hypothesis that GSH depletion could contribute to neuronal apoptosis in Parkinson's disease through oxidative stress and mitochondrial dysfunction.

Free radical scavenging properties of apomorphine enantiomers and dopamine: possible implication in their mechanism of action in parkinsonism

The influence of R(-) apomorphine, S(+) apomorphine and dopamine on the oxidation kinetics of two polyunsaturated fatty acids (PUFA) (cholesteryl linoleate (CL) and Trilinolein (TL)) was investigated. The oxidation was initiated by free radicals generated through thermal decomposition of 2.2'-Azobis(2-methyl-propionitrile) (AMPN) in phosphate buffer (pH 7.4) thermostated at 50 degrees C. The hydroperoxides formed were determined by iodine titration using a diode array spectrophotometer at 290nm. Both enantiomers of apomorphine as well as dopamine exerted an inhibitory effect. Tocopherol (alpha-tocopherol) and ascorbic acid were used as controls. The former inhibited while ascorbic acid facilitated the oxidation reaction. These results are discussed in relation with the possible role of oxidative injury in parkinsonism and the usefulness of apomorphine in elevating "on-off" episodes. On this basis, the non-dopaminergic enantiomer of apomorphine (S(+)-isomer) is put foward to test the importance of its radical scavenging properties in parkinsonism which could eventually lead to a therapeutic alternative with less side effects.

Melatonin rescues dopamine neurons from cell death in tissue culture models of oxidative stress

Dopamine (DA) neurons are uniquely vulnerable to damage and disease. Their loss in humans is associated with diseases of the aged, most notably, Parkinson's Disease (PD). There is now a great deal of evidence to suggest that the destruction of DA neurons in PD involves the accumulation of harmful oxygen free radicals. Since the antioxidant hormone, melatonin, is one of the most potent endogenous scavengers of these toxic radicals, we tested its ability to rescue DA neurons from damage/death in several laboratory models associated with oxidative stress. In the first model, cells were grown in low density on serum-free media. Under these conditions, nearly all cells died, presumably due to the lack of essential growth factors. Treatment with 250 microM melatonin rescued nearly all dying cells (100% tau+ neurons), including tyrosine hydroxylase immunopositive DA neurons, for at least 7 days following growth factor deprivation. This effect was dose and time dependent and was mimicked by other antioxidants such as 2-iodomelatonin and vitamin E. Similarly, in the second model of oxidative stress, 250 microM melatonn produced a near total recovery from the usual 50% loss of DA neurons caused by neurotoxic injury from 2.5 microM 1-methyl-4-phenylpyridine (MPP+). These results indicate that melatonin possesses the remarkable ability to rescue DA neurons from cell death in several experimental paradigms associated with oxidative stress.

Neuroprotective therapy for Parkinson's disease

The concept of neuroprotection relates to the fact that intervention may be able to interfere with the pathogenesis of neuronal cell death. Neuroprotective therapy may make it possible to delay disease progression or prevent the disease altogether. The pathophysiological mechanism of cell death in Parkinson's disease is unknown; however, hypotheses have been developed. The discovery that the toxin MPTP can cause Parkinson's disease both in humans and in animals strengthened the hypothesis that either exogenous or endogenous toxins may be involved in the mechanism of cell death in Parkinson's disease. The mechanism of MPTP toxicity has been elucidated, lending several possible mechanisms for therapeutic intervention in Parkinson's disease. Current data suggest that oxidative stress may play a prominent role in the pathogenesis of Parkinson's disease. It is possible that the generation of free radicals leads to neuronal cell death. There is also evidence that mitochondrial damage may play a role in the pathogenesis of Parkinson's disease. Other theories of possible pathogenesis include excitotoxicity, disturbances of calcium homeostasis, immunological mechanisms, and infectious etiologies. The first agent to be tested as a candidate for neuroprotection was the MAO-B inhibitor deprenyl. Evidence is reviewed for and against the theory that this drug is neuroprotective.

Neuronal vulnerability in Parkinson's disease

Although Parkinson's disease is characterized by a loss of dopaminergic neurons in the substantia nigra not all dopaminergic neurons degenerate in this disease. This suggests that some specific factors make subpopulations of dopaminergic neurons more susceptible to the disease. Here, we show that the most vulnerable neurons are particularly sensitive to oxidative stress and rise in intracellular calcium concentrations. Because both events seem to occur in Parkinson's disease this may explain why some dopaminergic neurons degenerate and other do not.

Oxidative stress and antioxidant therapy in Parkinson's disease

Parkinson's disease, known also as striatal dopamine deficiency syndrome, is a degenerative disorder of the central nervous system characterized by akinesia, muscular rigidity, tremor at rest, and postural abnormalities. In early stages of parkinsonism, there appears to be a compensatory increase in the number of dopamine receptors to accommodate the initial loss of dopamine neurons. As the disease progresses, the number of dopamine receptors decreases, apparently due to the concomitant degeneration of dopamine target sites on striatal neurons. The loss of dopaminergic neurons in Parkinson's disease results in enhanced metabolism of dopamine, augmenting the formation of H2O2, thus leading to generation of highly neurotoxic hydroxyl radicals (OH.). The generation of free radicals can also be produced by 6-hydroxydopamine or MPTP which destroys striatal dopaminergic neurons causing parkinsonism in experimental animals as well as human beings. Studies of the substantia nigra after death in Parkinson's disease have suggested the presence of oxidative stress and depletion of reduced glutathione; a high level of total iron with reduced level of ferritin; and deficiency of mitochondrial complex I. New approaches designed to attenuate the effects of oxidative stress and to provide neuroprotection of striatal dopaminergic neurons in Parkinson's disease include blocking dopamine transporter by mazindol, blocking NMDA receptors by dizocilpine maleate, enhancing the survival of neurons by giving brain-derived neurotrophic factors, providing antioxidants such as vitamin E, or inhibiting monoamine oxidase B (MAO-B) by selegiline. Among all of these experimental therapeutic refinements, the use of selegiline has been most successful in that it has been shown that selegiline may have a neurotrophic factor-like action rescuing striatal neurons and prolonging the survival of patients with Parkinson's disease.

Elevated cerebrospinal fluid levels of manganese superoxide dismutase in bacterial meningitis

We examined the mechanism of increase of manganese superoxide dismutase (Mn SOD) in the cerebrospinal fluid (CSF) in bacterial meningitis (BM). The elevated levels of Mn SOD in the CSF in BM, measured with an enzyme immunoassay method, were more prominent than those in aseptic meningitis (AM) and encephalitis (EN). In AM and EN Mn SOD levels well correlated with levels of neuron-specific enolase and S-100b protein, which are markers of damages to nervous tissues, but did not with any of them in BM. CSF concentrations of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha) were higher in BM than in AM and EN. From the serial measurements in BM, the peak values of these cytokines chronologically preceded or corresponded to those of Mn SOD. Immunohistochemically, a large number of the glial cells were stained for Mn SOD in the cerebral cortex from a patient with BM. By contrast, in the normal cerebral cortex, the glial cells were negative for Mn SOD staining. These results suggest that the marked increase of Mn SOD in the CSF in BM may be related to the increase of such cytokines as TNF-alpha and IL-1 alpha and that these cytokines may play a role in the induction of Mn SOD in nervous tissues.

Toxic effects of L-DOPA on mesencephalic cell cultures: protection with antioxidants

The toxicity of L-3,4-dihydroxyphenylalanine (L-DOPA) was studied in neuronal cultures from rat mesencephalon. The survival and function of DA neurons were assessed by the number of tyrosine hydroxylase-positive (TH+) cells and 3H-DA uptake and those non-DA neurons by the exclusion of Trypan blue and the high-affinity 3H-GABA uptake. L-DOPA was toxic for both DA and non-DA neurons. DA neurons were more severely affected than non-DA neurons after short periods of treatment and with exposure to a low dose of L-DOPA (25 vs. 100 microM) and less selectively affected after 1 or 2 days of treatment. After incubation with L-DOPA, a disruption of the neuritic network and an overall deterioration were observed, more evident for TH+ cells in the whole culture. Auto-oxidation to quinones is responsible in part for L-DOPA toxicity in non-DA neurons since the levels of quinones correlated well with the severity of cell death in the cultures. The damage of DA neurons took place before the rising of quinones, suggesting that quinones are not essential in L-DOPA toxicity for DA neurons. Antioxidants, such as ascorbic acid and sodium metabisulfite, completely prevented L-DOPA-induced quinone formation as well as the death of non-DA neurons. In contrast, they could only partially prevent the damage produced by L-DOPA in DA neurons. Mazindol, a selective inhibitor of DA uptake, protected TH+ cells from L-DOPA.

Reduced and oxidized forms of glutathione and alpha-tocopherol in the cerebrospinal fluid of parkinsonian patients: comparison between before and after L-dopa treatment

In the cerebrospinal fluid of untreated patients with Parkinson's disease (PD) the concentrations of reduced glutathione (GSH) and alpha-tocopherol (alpha-TOH) were unaltered but the concentration of oxidized glutathione (glutathione disulfide, GSSG) (P < 0.001), the GSSG/GSH ratio (P < 0.06), alpha-tocopherol quinone (alpha-TQ) (P < 0.001), and the alpha-TQ/alpha-TOH ratio (P < 0.01) were reduced significantly. In L-dopa-treated patients, the concentrations of GSH, GSSG, and the alpha-TQ concentration and the alpha-TQ/alpha-TOH ratio (P < 0.05) increased compared with untreated PD patients. These results suggest that oxidation of GSH and alpha-TOH is decreased in untreated PD patients, but is activated to a control level or more after L-dopa treatment.

Biochemistry of Parkinson's disease with special reference to the dopaminergic systems

The cardinal neurochemical abnormality in Parkinson's disease is the decreased dopamine content in the striatum, resulting from the loss of dopaminergic neurons in the mesencephalon. Precise analysis of the dopaminergic neurons in the midbrain demonstrates, however, that this cell loss is not uniform. Some dopaminergic cell groups are more vulnerable than others. The degree of cell loss is severe in the substantia nigra pars compacta, intermediate in the ventral tegmental area and cell group A8, but nonexistent in the central gray substance. This heterogeneity provides a good paradigm for analyzing the factors implicated in this differential vulnerability. So far, the neurons that degenerate have been shown to contain neuromelanin, high amounts of iron, and no calbindin28K, and to be poorly protected against oxidative stress. By contrast, the neurons that survive in Parkinson's disease are free of neuromelanin, calbindinD28-positive, contain low amounts of iron, and are better protected against oxidative stress. The analysis of the pattern of cell loss in Parkinson's disease may thus bring new clues as to the mechanism of nerve cell death in Parkinson's disease.

Autoradiographic distribution of mu opioid receptors in the brains of Cu/Zn-superoxide dismutase mice

Superoxide dismutase (SOD) is an important free radical scavenging enzyme which dismutates the superoxide anion radical. We have evaluated the role of SOD in the regulation of opioid receptors by comparing the concentration of mu opioid receptors labeled with [3H]DAGO (Tyr-D-Ala-Gly-NMe-Phe-Gly-ol) in SOD-transgenic (SOD-Tg) mice and their non-transgenic (Non-Tg) littermates. SOD-Tg mice had higher maximal binding capacity (Bmax) in the shell division of the nucleus accumbens (NAc-shell) in comparison to Non-Tg littermates. There were no differences in Bmax in mu receptors in the core subdivision of the nucleus accumbens (NAc-core). There were no significant differences in receptor affinity (Kd) in either the NAc-shell or in the NAc-core. Moreover, there were no significant differences in either Bmax or Kd in the matrices nor in the patches of any of the striatal subdivisions. However, in a fashion similar to the situation in the NAc-shell, [3H]DAGO binding in the substantia nigra pars compacta (SNpc), the ventral tegmental area (VTA), and the ventral part of the central grey was significantly higher in the SOD-Tg mice in comparison to Non-Tg mice. The present results are discussed in terms of their support for a possible involvement of free radicals in the differences observed in various regions of the SOD-Tg and control mice, which differ in their ability to scavenge the superoxide anion.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative stress: free radical production in neural degeneration

It is not yet established whether oxidative stress is a major cause of cell death or simply a consequence of an unknown pathogenetic factor. Concerning chronic diseases, as Parkinson's and Alzheimer's disease are assumed to be, it is possible that a gradual impairment of cellular defense mechanisms leads to cell damage because of toxic substances being increasingly formed during normal cellular metabolism. This point of view brings into consideration the possibility that, besides exogenous factors, the pathogenetic process of neurodegeration is triggered by endogenous mechanisms, either by an endogenous toxin or by inherited metabolic disorders, which become progressively more evident with aging. In the following review, we focus on the oxidative stress theory of neurodegeneration, on excitotoxin-induced cell damage and on impairment of mitochondrial function as three major noxae being the most likely causes of cell death either independently or in connection with each other. First, having discussed clinical, pathophysiological, pathological and biochemical features of movement and cognitive disorders, we discuss the common features of these biochemical theories of neurodegeneration separately. Second, we attempt to evaluate possible biochemical links between them and third, we discuss experimental findings that confirm or rule out the involvement of any of these theories in neurodegeneration. Finally, we report some therapeutic strategies evolved from each of these theories.

Transgenic and knock-out mice: models of neurological disease

Besides providing useful model systems for basic science, studies based on modification of the mammalian germ line are changing our understanding of pathogenetic principles. In this article, we review the most popular techniques for generating specific germ line mutations in vivo and discuss the impact of various transgenic models on the study of neurodegenerative diseases. The "gain of function" approach, i.e., ectopic expression of exogenous genes in neural structures, has deepened our understanding of neurodegeneration resulting from infection with papova viruses, picorna viruses, and human retroviruses. Further, inappropriate expression of mutated cellular molecules in the nervous system of transgenic mice is proving very useful for studying conditions whose pathogenesis is controversial, such as Alzheimer's disease and motor neuron diseases. As a complementary approach, ablation of entire cell lineages by tissue-specific expression of toxins has been useful in defining the role of specific cellular compartments. Modeling of recessive genetic diseases, such as Lesch-Nyhan syndrome, was helped by the development of techniques for targeted gene deletion (colloquially termed "gene knock-out"). Introduction of subtle homozygous mutations in the mouse genome was made possible by the latter approach. Such "loss of function" mutants have been used for clarifying the role of molecules thought to be involved in development and structural maintenance of the nervous system, such as the receptors for nerve growth factor and the P0 protein of peripheral myelin. In addition, these models are showing their assets also in the study of enigmatic diseases such as spongiform encephalopathies.

Is brain superoxide dismutase activity increased following chronic treatment with 1-deprenyl?

L-deprenyl, a specific MAO-B inhibitor, has been proposed to possess a neuroprotective effect. The mechanism of such an effect is unclear. L-Deprenyl has been found to increase rat striatal superoxide dismutase (SOD) activity, which inactivates singlet oxygen. It would be very interesting to know how such activation occurs and whether or not other MAO inhibitors also have such an effect. We have analyzed rat striatal SOD activity using a very sensitive nitrite method and an immunological procedure. The effect of different doses and time of treatment with 1-deprenyl and M-2-PP (2-pentyl-N-methyl-propargylamine), a new highly potent, selective and non-amphetamine-like MAO-B inhibitor, on the rat brain has been investigated. We were unable to detect any increase of SOD activity in the rat striata and cerebral cortex nor any increase in the concentration of immunoreactive SOD antibody in the cortex following chronic treatment with 1-deprenyl and M-2-PP. It remains to be substantiated as to whether or not 1-deprenyl can enhance SOD levels.

The effect of pergolide and MDL 72974 on rat brain CuZn superoxide dismutase

It has previously been shown that both the dopamine receptor agonist, pergolide, and the monoamine oxidase inhibitor, (-)-deprenyl, can cause induction of CuZn superoxide dismutase in the rat striatum. We have now confirmed this effect of pergolide (0.04 mg/kg i.p.) as being localised to the striatum, but not the cerebellum, and shown it to take 3 weeks to develop. Furthermore, we have found that MDL 72974, a more specific monoamine oxidase inhibitor than (-)-deprenyl, failed to bring about such an induction either at a low selective monoamine oxidase B inhibitory dose, or at a higher non-selective dose.

A radical hypothesis for neurodegeneration

Point mutations in the cytosolic Cu/Zn superoxide dismutase (SOD-1) gene have been detected in association with familial amyotrophic lateral sclerosis (FALS). SOD clears superoxide radical and is one of the body's principal defense mechanisms against oxygen toxicity. The finding of SOD variants in FALS is consistent with the hypothesis that free radicals contribute to the pathogenesis of FALS, and possibly to the pathogenesis of other neurodegenerative disorders such as Parkinson's disease, in which there is substantial evidence of oxidant stress. The implication of free radicals in the pathogenesis of neurodegenerative disorders raises the possibility that antioxidants might provide neuroprotective therapy.

Preferential expression of superoxide dismutase messenger RNA in melanized neurons in human mesencephalon

The copper-zinc-dependent superoxide dismutase messenger RNA expression was studied at cellular level by in situ hybridization, using a 35S-labelled complementary DNA probe homologous to human copper-zinc-dependent superoxide dismutase messenger RNA, in the dopaminergic neuron-containing areas of the human mesencephalon (the substantia nigra pars compacta, ventral tegmental area, central gray substance and peri- and retrorubral region corresponding to catecholaminergic cell group A8). The autoradiographic labelling signal was localized in neurons. No detectable hybridization signal could be found in the glial cells. Copper-zinc-dependent superoxide dismutase messenger RNA was detected in melanin-containing neurons as well as in non-melanized neurons. Quantification at cellular level, taking the autoradiographic silver grain density as an index of the abundance of copper-zinc-dependent superoxide dismutase messenger RNA, indicated that hybridization level was higher in the melanized than in the non-melanized neurons within a region. Among melanized neurons, cellular copper-zinc-dependent superoxide dismutase messenger RNA content was lowest in the neurons of the substantia nigra. No significant difference in levels of transcripts was evidenced between the groups of non-melanized neurons. The data suggest that the abundance of copper-zinc-dependent superoxide dismutase messenger RNA is higher in the mesencephalic neurons containing neuromelanin compared to other neurons. Thus, the melanized neurons have a particular defence system against oxygen toxicity, which may represent a basis for their preferential vulnerability to Parkinson's disease.

Glutathione peroxidase, glial cells and Parkinson's disease

Hyperoxidation phenomena are suspected to be involved in dopaminergic cell death in Parkinson's disease, which affects preferentially the neuromelanin-containing dopaminergic neurons of the substantia nigra. Glutathione peroxidase is the major protective enzyme against hydrogen peroxide toxicity. The distribution of glutathione peroxidase-containing cells was investigated by immunohistochemistry in the midbrain of four control subjects and four patients with Parkinson's disease. (1) Glutathione peroxidase-like immunoreactivity was detected exclusively in glial cells. (2) In control brains, the density of glutathione peroxidase-positive cells was higher in the vicinity of the dopaminergic cell groups known to be resistant to the pathological process of Parkinson's disease. (3) In Parkinson's disease, an increased density of glutathione peroxidase-immunostained cells was observed, surrounding the surviving dopaminergic neurons. The increase in glutathione peroxidase-containing cells was correlated with the severity in dopaminergic cell loss in the respective cell groups. The data suggest that in control brains, a low density of glutathione peroxidase-positive cells surround the dopaminergic neurons the most vulnerable to Parkinson's disease, and that in parkinsonian brains, the increased number of glutathione peroxidase-positive cells may contribute to protect neurons against pathological death. Thus, the amount of glutathione peroxidase protein-containing cells may be critical for a protective effect against oxidative stress, although it cannot be excluded that the level of the enzyme activity remains the crucial factor.

Peripheral blood cell activities of monoamine oxidase B and superoxide dismutase in Parkinson's disease

Monoamine oxidase type B (MAO-B) and superoxide dismutase (SOD) are two enzyme systems that are potentially relevant to an oxidative stress model of Parkinson's disease (PD) causation. Activities of MAO-B in platelets (nmol/10(8) cells/hr) and total SOD in lymphocytes (U/mg protein) were assayed among 28 cases of idiopathic PD and 22 controls. As anticipated, MAO-B was lowest in PD cases on selegiline (L-deprenyl) therapy (mean 1.10). There was a slight deficit of MAO-B among male cases not taking selegiline compared to controls (3.78 vs. 4.15), but the opposite trend was observed for females (6.18 vs. 4.16). SOD was slightly higher in cases (7.40), than controls (6.81). Excess SOD among PD cases was seen irrespective of gender, age, or selegiline treatment, although none of the differences was statistically significant. Future research on SOD should take advantage of the availability of assays specific for the cytosolic and mitochondrial forms of the enzyme.

Age-related changes in antioxidant enzymes and lipid peroxidation in brains of control and transgenic mice overexpressing copper-zinc superoxide dismutase

The aim of our study was first to obtain a comprehensive profile of the brain antioxidant defense potential and peroxidative damage during aging. We investigated copper-zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), seleno-dependent glutathione peroxidase (GSH-PX), glutathione reductase (GSSG-R) activities, endogenous and in vitro stimulated lipid peroxidation in 40 brains of control mice divided into 3 age groups: 2 months (young), 12 months (middle-aged) and 28 months (old). We found a positive correlation between age and activities of CuZnSOD (r = 0.47; P < 0.01) and GSH-PX (r = 0.72; P < 0.0001). CuZnSOD and GSH-PX activities are independently regulated during brain aging since temporal changes of these two enzymes do not correlate. No modification in MnSOD activity and basal lipid peroxidation was observed as a function of age. Nevertheless, stimulated lipid peroxidation was significantly higher at 12 months (6.53 +/- 0.71 mumole MDA/g tissue) than at 2 months (5.69 +/- 0.90) and significantly lower at 28 months (5.13 +/- 0.33) than at 12 months. Second, we used genetic manipulations to construct transgenic mice that specifically overexpress CuZnSOD to understand the role of CuZnSOD in neuronal aging. The human CuZnSOD transgene expression was stable during aging. The increased CuZnSOD activity in the brain (1.9-fold) of transgenic mice resulted in an enhanced rate of basal lipid peroxidation and in increased MnSOD activity in the 3 age groups. Other antioxidant enzymes did not exhibit modifications indicating the independence of the regulation between CuZnSOD and glutathione-related enzymes probably due to their different cellular localization in the brain.

Toxicity of 1-methyl-4-phenylpyridinium derivatives in Escherichia coli

Several derivatives of 1-methyl-4-phenylpyridinium (MPP+), i.e., 1-methyl-4-(4'-nitrophenyl)pyridinium (1), 1-methyl-4-(4'-cyanophenyl)pyridinium (2), 1-methyl-4-(3'-nitrophenyl)pyridinium (3), 1-methyl-4-(4'-chlorophenyl)pyridinium (4), 1-methyl-4-(4'-acetamidophenyl)pyridinium (5), and 1-methyl-4-(4'-aminophenyl)pyridinium (6), were synthesized in order to compare their toxicity with that of paraquat (PQ2+) in Escherichia coli. Addition of compounds 1, 2, and 3 to aerobic E. coli cell suspensions caused extracellular ferricytochrome c reduction, which was inhibited by superoxide dismutase in the same manner as that in the case of PQ2+. The rate of the ferricytochrome c (cyt. c) reduction was in the order of PQ2+ greater than 1 greater than 2 greater than 3, which is the same as that of the redox potentials of these compounds. On the other hand, MPP+, 4, 5, and 6, which have more negative potentials, had no effect on the cyt. c reduction. Compound 1 inhibited the growth of E. coli under aerobic conditions, but not under anaerobic conditions. The results show that compound 1 can act as a mediator for production of superoxide (O2-.), which seriously injures E. coli cells. However, though compounds 2 and 3 catalyzed the production of O2-. in E. coli cells, their activity of O2-. production was much lower than that of compound 1 or PQ2+. Thus, compound 3 had no effect on growth or survival of E. coli at 1 mM, while compounds 2 and 4 had both bacteriostatic and bacteriocidal effects which were independent of dioxygen (O2). The results show that the toxic mechanism is different from that of compound 1. MPP+, 5, and 6 had no effect on growth of E. coli. This paper shows that compound 1 is a novel enhancer of intracellular superoxide production, though the mechanism of toxicity of compounds 2 and 4 is not clear yet. The results suggest that the redox potential is a crucial factor for manifestation of the activity.

Receptor alterations in manganese intoxicated monkeys

The density of four different receptors and one marker of dopamine uptake sites were analyzed in monkey brains after manganese exposure (0.1 g manganese per month during 26 months, a dose comparable to that workers might inhale in dusty environments) by means of quantitative receptor autoradiography. The binding of 3H-mazindol to the dopamine uptake sites was reduced by 75% in both the head of the caudate nucleus and putamen, while it remained unchanged in the other regions analyzed. The binding of the D1 receptor ligand 3H-SCH 23,390 was reduced about 45% in the same areas as mazindol binding, while the density of D2 receptors was unaffected. The muscarinic acetylcholine receptors as well as GABAA receptors remained also unchanged in all brain areas analyzed after manganese exposure. Thus the dopaminergic neurons must be considered to be vulnerable to manganese concentrations attainable in the work environment. Our results also indicate that postsynaptic structures containing D1 receptors are sensitive while cells containing D2 receptors are either spared or compensated for by up-regulation of the number of receptors on remaining sites.

Cu/Zn superoxide dismutase mRNA and enzyme activity, and susceptibility to lipid peroxidation, increases with aging in murine brains

To protect against reactive oxygen species, prokaryotic and eukaryotic cells have developed an antioxidant defence mechanism where O2- is converted to H2O2 by superoxide dismutase (Sod), and in a second step, H2O2 is converted to H2O by catalase (Cat) and/or glutathione peroxidase (Gpx). If Sod levels are increased without a concomitant Gpx increase, then the intermediate H2O2 accumulates. This intermediate could undergo the Fenton's reaction, generating hydroxyl radicals which may lead to lipid peroxidation in cells. In this study, we investigate the expression of Sod1, Gpx1 and susceptibility to lipid peroxidation during the aging process in mouse brains. We demonstrate that the mRNA levels and enzyme activity of Sod1 are higher in brains from adult mice compared to neonatal mice. Furthermore, we show that a linear increase in Sod1 mRNA and enzyme activity occurs with aging (1-100 weeks). On the contrary, we find that the mRNA and enzyme activity for Gpx1 does not increase with aging in mouse brains. In addition, our results demonstrate that the susceptibility of murine brains to lipid peroxidation increases with aging. The data in this study are consistent with the notion that reactive oxygen species may contribute to the aging process in mammalian brains. These results are discussed in relation to the normal aging process in mammals, and to the premature aging and mental retardation in Down syndrome.

Serum antioxidant enzyme activity in Parkinson's disease

The activities of superoxide dismutase (SOD; EC 1.15.1.1) and glutathione peroxidase (GSHPx; EC 1.11.1.9), the enzymes that metabolize the superoxide anion and hydrogen peroxide, respectively, were measured in serum from healthy subjects and patients with Parkinson's disease (PD). The activities of SOD and GSHPx in patients with PD were higher than those in normal healthy individuals. These results suggest that the increased activities of these enzymes could be due to oxidative stress in the initial stages of this disease.

Cellular clones and transgenic mice overexpressing copper-zinc superoxide dismutase: models for the study of free radical metabolism and aging

Down's Syndrome (DS), the most frequent of congenital birth defects, results from the trisomy of the chromosome numbered 21 in all cells of affected patients. This disease is characterized by developmental anomalies, mental retardation and features of rapid aging, particularly in the brain where the occurrence of Alzheimer's disease (AD) is observed in all trisomy 21 patients over the age of 35. Elucidation of the biological mechanisms leading to brain aging in DS might provide new insight into the understanding of brain aging and AD in normal people. Copper-zinc superoxide dismutase (CuZnSOD) is one of the genes encoded by chromosome 21. As a consequence of gene dosage excess, CuZnSOD activity and protein are increased by 50% in all DS tissues. The level of CuZnSOD protein and mRNA is particularly high in hippocampal pyramidal neurons susceptible to degenerative processes in AD and in dopaminergic melanized-neurons vulnerable in Parkinson's disease. Increased CuZnSOD activity in these age-related neurodegenerative disorders might result in H2O2 overproduction and subsequently promote peroxidative damages within cells. Increase of seleno-dependent glutathione peroxidase (Se-GPx) in DS cells supports this concept. In order to test this hypothesis, cell and animal models of CuZnSOD overexpression have been designed. In cells transfected with the human CuZnSOD gene, and increased Se-GPx activity is observed, a situation which mimics DS. In mice transgenic for the human CuZnSOD, the expression pattern of the transgene in the brain is similar to that in humans, and we can observe an increased peroxidation in this tissue. These data, like others in the literature, support the hypothesis that excess CuZnSOD induces an imbalance in the regulation of oxygen-derived free radical production which might result in peroxidative brain damage and possibly contribute to accelerated aging and age-related neuropathology.

Why are nigral catecholaminergic neurons more vulnerable than other cells in Parkinson's disease?

Although the cause of neuronal death in Parkinson's disease remains unknown, a hyperoxidation phenomenon has been implicated as a potential cytotoxic mechanism. Catecholaminergic neurons containing neuromelanin, an autoxidation byproduct of catecholamines, are more vulnerable in Parkinson's disease than nonmelanized catecholaminergic neurons. High levels of CuZn superoxide dismutase mRNA have been observed in the substantia nigra, suggesting that high levels of oxygen free radicals are indeed produced in the structure. Catecholaminergic neurons surrounded by a low density of glutathione peroxidase cells are more susceptible to degeneration in Parkinson's disease than those well protected against oxidative stress. The nigral content in iron, a compound that exacerbates the production of free radicals in catecholaminergic neurons, is increased in Parkinson's disease. Altogether these data suggest that hyperoxidation may participate in the selective vulnerability of catecholaminergic neurons in Parkinson's disease.